Polymorph Substrate

Blobs #2 and #3 both broke free of the base before the build completed. This prompted me to search for a substrate that would hold the build in place and be relatively easy to remove afterward. Tried a bunch of things, most of which don't work.

One thing I tried shows promise. I melted some polymorph (aka friendly plastic) and flattened it into a sheet roughly 1mm thick. I ran a layer on this, holding it down with my hands and trying not to burn my fingers on the extruder. It worked fairly well, considering the sheet was a bit uneven. A polymorph sheet has the additional advantage of being reusable. You can melt it in hot water and re-form it.

Now I just need to find a way to make flat sheets of polymorph.

Blob #1

Ran into some problems with the extruder. It's very hard to keep it extruding at a consistent rate. Currently using compression springs tightened down pretty hard. That seems to keep things going.

Spent some time playing with the various settings. Documentation on what each setting does can be found here. Noticed that, with my version of the host software (0.8.3), setting Extruder0_OffsetZ to 0 caused occasional I/O errors. Setting it to 1 seemed fine, though.

The blob pictured above is supposed to be Minimug.stl and it's roughly the right size and shape. The key word here is "roughly". This run was done at the highest extruder speed I could manage, the heater running a bit hot and no fan attached. End result? It's a bit wibbly and it leaks. Definitely not toast-worthy.

Got some good information out of it, though:
A margarine container lid works well as a build raft. The plastic sticks to it nicely.
The parts that printed correctly are quite solid. Very good adhesion between layers.
The X, Y and Z scaling's pretty close. Might need a bit of tweaking but not much.

Next step will be to run it again at a slower speed.

If At First You Don't Succeed...

...get out the hacksaw. The extruder broke again. This time it was the flexible shaft snapping. Decided to eliminate it entirely and have the motor drive the screw directly. Added a filament guide made from a bent paperclip to keep the filament away from the motor.

Shakedown

Attached the extruder board. Left the extruder off and added a resistor to simulate the thermistor. Loaded the minimug model and ran a build to see if it could make it through without shaking apart. The Y motor coupling came loose but everything else seemed to work reasonably well. Drilled out a pit for the Y coupling grub screw. Should keep it from slipping.

The good news is that it finished the build without a) crashing the host software, b) coming apart or c) bursting into flames.

Cleanup

Picked up some cable clamps to attach the PCBs to the frame. Used some zip ties to clean up the wiring.


Attached a pencil to the head bracket and used the line tool to draw 3-4-5 triangles (actually 60x80mm). The pencil was a bit wobbly but it was enough to verify that my XY frame is square.

Axis-Backwards

Hooked up the electronics. Just the comms and 3 stepper drivers. Left the extruder board out of the loop for now. Don't seem to have any PCB mounts and the diagonals I would've mounted them on aren't installed, so I just left them hanging in a rat's nest arrangement while I did a systems check.

Fired up the host app and opened the stepper exerciser. First thing I noticed was that the Y axis kept moving in the same direction no matter where I moved the slider. Turned out to be a mechanical problem with the Y opto. It was reading "home" even when not blocked. Once I fixed that, I noticed that both the X and Y axes were running backwards. When I moved the slider in the positive direction, the stepper would move the head away from the corresponding opto. I reversed the order of the wires on both motor connectors and that seemed to fix it.

This is very odd because, at the time, the instructions indicated that the Y and Z motors should be wired one way and the X should be wired opposite. As it sits now, I've got the X and Z wired one way and the Y opposite. The instructions have since been edited and there's now only a single note indicating that the X stepper is the odd one out. There used to be a table showing the wiring of the Y and Z versus the X but it's no longer in the wiki. I managed to find an archived version of the table and I've edited it to the wiring arrangement I'm currently using:

Pin (X & Z axes)	Pin (Y axis)	Colour
1	4	Red
2	3	Black
3	2	Green
4	1	Yellow

Note: The above is the wiring for the Nanotec motors.

The good news is that the Z axis worked perfectly the first time. I had made three mods to it:
1. Used a metal motor coupler
2. Added a belt tension idler
3. Removed the backlash springs and screws

The end result is a Z axis that moves smoothly with very little strain on the motor. As far as I can tell, the weight of the bed is more than enough to prevent backlash.

After a bit of fiddling, I worked out that I'm getting roughly 10 steps per mm on X and Y and 300 steps per mm on Z. Total travel on X and Y is about 230 mm and Z is at least 90, depending on where the nozzle ends up.

Opto Flags

Installed the optos and flags. Had a little trouble working out the Z flag. The instructions show this configuration:


...but I couldn't find the Z flag base. I had a few leftover bits but not that one. I opened up Art of Illusion and started looking at the models. Found "z flag adjuster housing", which looked like one of my leftover bits. So, I googled "z flag adjuster" and found this:

From there, I assembled something that looked like that from the parts I had on hand and bolted it to the bed. Looks about right.

Squaring Up

Added the diagonal ties to the sides. I did only one per side, hence the extra tie brackets for the tension idler. I had to shim the 5/16" rod in order to get a tight fit.

Squared up the X, Y and Z. Didn't have a squaring jig, so I did a lot of tweak-and-measure. I haven't added the fan or extruder. Going to hold off on that until later.

XYZ

Installed the Y axis assembly. The cobbled-together Y motor coupling fits, provided I put the drive pulley on backwards (collar away from motor).

Ran into a problem with the Z belt. It ended up a bit loose. Rather than take it apart and redo the whole thing, I built a tension idler out of spare parts (scrap studding, washers, nuts, diagonal tie brackets, compression spring, pulley). Seems to keep things from slipping.

Tension

Installed the base diagonals. Pretty straightforward. The tie brackets from BitsFromBytes don't have embedded nuts but the intent is to tighten the nuts on the diagonals until the plastic distorts enough to grip the uprights. Seems to work just fine.

Spliced together a Z belt. Ended up sanding down the belts before gluing them together. Seems to hold better that way. Used a blob of polymorph to make a splicer.

Wrapped a zip tie around the Z motor to hold it steady.

Top Frame

Added the top frame. Verified that all four sides were the same length. Slid it down onto the Z studding to square up the bed. Tightened the bed bolts.


Raised the top frame to its proper height and locked it off. Noticed that one of the Z studding assemblies was missing a nut and washer. In the middle. Bugger. Wound the studding up as high as possible, slipped it out of the corner block, removed half the nuts, washers, etc. Threaded the parts back on, double-checking the parts as I put them on. Wound the studding back into place.


Measured the height of the Z drive pulley above the corner block. Adjusted the other four pulleys to the same height. Tightened up the nuts on the four Z studding assemblies, adding grease where it seemed appropriate.

This image also shows the improvised motor coupling. Seems to work reasonably well. Have to see how it does under load.

Bed Time

Cut, drilled and installed the bed. The bed is 400mm square and 12mm thick. That translates to about 15.75" square and 1/2" thick. I bought a 24x48x1/2" sheet of MDF and cut it down to size.

The holes are 5.4mm and 7mm. Meh, call it 7/32" and 1/2". While drilling the holes, I put a piece of scrap under the sheet and drilled through both. Makes for cleaner exit holes. Here's a pic of the exit holes in the bed (green) and the scrap (red).


Here's the bed installed with all 12 bolts (loosely) in place. There weren't any bed clamps in the parts kit, so I'm assuming they aren't needed.

Going Vertical

Finished the 3 studding idlers and the studding drive. Attached them to the bottom frame. Mounting the motor's a real pain. I had to take it apart and redo it a couple times before I got it right. The cobbled-together motor coupling sees to work just fine.

Coupling

I picked up some 5/16" threaded rod couplings (7/8" long) and some 6-32 grub screws at the hardware store. The inside diameter of the threads is just slightly larger than the motor shaft. I bored out one end with a 5/16" bit to a depth of about 1/4", then drilled and tapped two 6-32 holes along the length. The grub screw for the 5/16" bore is about 1/8" from the end. I made two of these: one for the Y motor; one for the Z.

The image here is a test fit using some scrap rod. I've put the Y drive pulley on backwards to give myself more room for the coupling. The motor shaft isn't quite as snug as I'd like but it should do.

The current plan is to use the McMaster pulleys and belts. I've bored all six pulleys to 5/16". One of the Y pulleys is slightly off center. I may need to replace it.

Springs

Found some compression springs at the hardware store. They were over with the screen door accessories. There are two pair in the blister pack: 1/2"x1 1/2" and 7/16"x 2 1/8". I used the longer ones.

Parts Problems

Started on the studding idlers. Looks like the Z idler pulley size has changed since I ordered my parts. Using the plastic ones from BitsFromBytes instead of the aluminum ones from McMaster. Those had the wrong bore (1/4") anyway.

Also looks like the springs I got from McMaster are the wrong size. They're 9/32" OD, which makes them smaller that the studding they're supposed to slip over. I can probably find some reasonable springs somewhere.

It also looks like the toothed belts and pulleys I got from McMaster are a different pitch than the RP'd pulleys. Not sure what I'm going to do about that.

XY Frames

Assembled the two XY frames. Lessons learned:

• It's easy to overtighten the grub screws and crack the plastic.
• When assembling the top frame, you need to run the two upper rods through the X axis assembly.
• The "Bearing insert 180 X" in the X axis assembly is the one with the oblong hole.
• It's really hard to push an 8mm rod through a 5/16" hole.

Here are some pictures of the two frames stacked on top of each other. Note that all four corner blocks on the top frame have the face with 4 holes facing inward, along the line of the X axis. As far as I can tell, this will allow me to mount the Y bearing brackets correctly.